Multi-cell communication systems are well known. They are typically comprised of a plurality of stationary cell sites and a plurality of mobile subscriber units. The cell sites, distributed across a geographic region, contain base radios which are all linked to switching and control devices. A particular cell site provides communication to the subscriber units within its service coverage area, or cell. By interconnecting and distributing cell sites in an adjacent fashion, a much broader, combined coverage area can be created. Subscriber units anywhere in this combined area, then, are able to obtain communication, both inside and outside the communication system, via at least one of the cell sites and, thereby, via the system switching and control devices. As subscriber units travel from the coverage area of one cell site to another an ongoing communication must be handed-off to be maintained. A number of techniques exist and are well known for performing such hand-offs. Mobile-assisted hand-off (MAHO) is one such technique.
In general, when a communication is established in a multi-cell communication system, the system devices must allocate communication resources to support the communication. In such systems, there are only a limited number of communication channels available between a cell site and its controller. One communication channel from this pool, if available, is allocated to establish the communication. Now, if the subscriber unit involved in the communication must hand-off, the original communication channel is also handed-off to a second communication channel. This is necessary because, today, such communication channels are dedicated or assigned to particular cell site base radios on a permanent basis, and handing-off involves switching from one base radio to another. So to hand-off, the second communication channel must be allocated just as the original channel was. If a second channel is not available, the hand-off can not be performed and the communication may be dropped as a result. When communication is dropped because hand-offs can not be performed, the effective system coverage suffers. Also, if a second channel is available and is allocated, the system now has two communication channels in use for one communication until the hand-off is completed. In a busy system this may prevent another communication from being established, thus, reducing the system capacity. And finally, handing-off to the second communication channel may require a temporary muting of the communication until the hand-off is completed.
A need exists, therefore, for an apparatus and method for allocating communication resources in such a manner as to limit the problems of reduced system coverage, reduced system capacity, and muting during hand-offs.